Today, most communication systems involve a number of system-cards. Such cards are usually manufactured as so-called printed circuit boards (PCBs). Usually, some of the system-cards, which are called daughter boards, are assembled together on a rigid system-card called the backplane, or mother board.
The daughter boards usually extend parallel with each other and are interconnected together via the backplane, which extends perpendicular to them. There are several practical advantages to such a configuration: Easy insertion, removal, and replacement of the daughter-boards.
Because of the ever increasing requirements in data rates in communication systems, due for example to the Internet, the limits of using electrical communications between printed circuit boards (PCB) are being reached. It has become difficult to guarantee good signal integrity when transferring information at high frequencies (e.g. 25 Gb/s or higher) through electrical lines between two electrical components such as a printed circuit board.
To respond to this bandwidth demand, high-speed systems now use optical waveguide light to transfer light-carried information.
Light enables to improve the transfer of information between two points since light is less sensitive to interference phenomenon. High speed systems are now being built with optical layers (optical fibres or planar waveguides) incorporated in replacement of the electrically-conducting metal. An optical layer is disposed parallel to the average plane of the backplane. An other optical layer is disposed parallel to the average plane of the daughter board.
The daughter board may comprise a set of opto-electronic components which will either emit or detect light transmitted through its optical layer. U.S. Pat. No. 7,149,376 discloses one such embodiment.
With the stringent requirements for miniaturization, together with the ever-increasing demands for higher transmission rates, attention is now turning to the efficient thermal management of such systems.